Soil organic carbon, macro- and micronutrient changes in soil fractions with different lability in response to crop intensification

Abstract

Soils under no tillage have experienced unfavorable changes, mainly due to current agricultural practices that consist in monocultures that leave little residue cover. The inclusion of grass as cover crops during the winter season could be a sustainable strategy to increase crop intensification in sequences where soybean predominates, helping to maintain soil fertility, organic matter levels and enhance soil physical properties. The aim of this research was to evaluate the effects of 8 years of sustainable crop intensification (by increasing the proportion of cereals in crop rotations) on soil organic carbon, macro- and micronutrients associated with granulometric fractions of different lability in a Typic Argiudoll of the Rolling Pampa, Argentina. The experiment included two crop sequences commonly used in this area: soybean-soybean (S-S) and maize-soybean-wheat/soybean (M-S-W/S) combined with the inclusion of wheat (Triticum aestivum L.) as cover crop (CC) in winter. The intensification sequence indices (ISI) were 0.39, 0.69, 0.55 and 0.64 for S-S, S-CC-S, M-S-W/S and M-CC-S-W/S, respectively. The carbon measured in the coarse particulate fraction (Pcf) in the 0–5 cm soil depth was 3 times larger in S-CC-S than in S-S. Cropping intensity also modified N, S, P, Ca and Mn in the Pcf with no changes in Mg, K, Zn, Fe and Cu contents. Among the carbon fractions studied, only the carbon measured in the Pcf and the easy mineralizable carbon estimated by the soil respiration in the first soil layer (0–5 cm), were positively correlated with the ISI. In the present study, 8 years under sustainable crop intensification were sufficient to show changes in the mineral associated fraction (Maf). Increases in the C in the Maf in maize legume-based rotation, suggest SOC accumulation in more stable carbon pools.